Peristaltic pump

ABSTRACT

A peristaltic pump with three coaxial cylindrical components; a high-modulus rod contained within a piezoelectric tube, which in turn is contained within a cylindrical pressure casing, which may the casing of a hydraulic cylinder. The casing is filled with ERF. The piezoelectric tube has a plurality of electrode bands attached to its outer surface and is coated on its interior with an electrically conductive material. The electrodes are voltage-activated to cause certain portions of the tube to expand and others to contract, resulting in peristaltic action. The applied voltage also causes the ERF to form a gel state both inside and outside of the piezoelectric tube.  
     A second embodiment includes a second set of electrode bands added to the interior of the casing, and a third set of electrode bands is added to the outside of the high-modulus rod.  
     A method of incorporating the peristaltic pump into the piston of a hydraulic cylinder thereby forming a self-contained electrically-powered hydraulic actuator.  
     An improved power supply that switches the polarity of the electrodes in a stepped fashion by transferring the associated charge through an inductor and drawing lost energy from a voltage source.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to peristaltic pumps and, more particularly, to a piezoelectric peristaltic pump with a non-contacting seal formed by solidification of electrorheological fluid (ERF) and methods of incorporating this pump into a hydraulic cylinder thereby forming a self-contained electrically-powered actuator. The present invention also relates to an improved power supply for use with that pump and other devices having similar electrical demands.

[0003] 2. Discussion

[0004] Modern vehicles with multiple moving parts, such as aircraft having multiple movable control surfaces, typically use hydraulic actuators supplied by a hydraulic pump acting through a complicated high pressure hydraulic system to control movement of such surfaces. Such systems have several disadvantages, including their weight, susceptibility to damage, and cost of maintenance. It therefore would be desirable to replace such systems with a compact, lightweight, distributed, all-electric system, which would save weight by eliminating the high-pressure piping and central hydraulic pump. Attempts to design such systems based on integrating a hydraulic pump and hydraulic actuator into a single package have been made. However, all known designs suffer from significant inherent limitations. These systems are far larger, heavier, and more complex than the conventional hydraulic cylinders they replace. Such systems typically use check valves or control valves to direct the flow of hydraulic fluid. In addition, such systems use an input stroke to draw oil into the pump volume and an output stroke to compress and expel the hydraulic fluid, resulting in inefficiencies, as fluid is left in the volume after the output stroke expands, reducing the amount of oil that can be drawn in during the input stroke.

[0005] There is therefore a need for a pump that can be integrated directly into a hydraulic cylinder with little increase in size or weight as compared to a conventional cylinder Such a pump should be reversible and operate without contacting seals that can wear or valves that add complexity and weight. It should also operate in a continuous manner without input and output strokes that add inefficiency. Finally, there is a need for a simple and inexpensive power supply that can drive this pump efficiently.

[0006] It is known to use piezoelectric materials to create contacting seals between concentric cylinders and thereby to form a peristaltic pump (see, e.g., U.S. Pat. No. 4,115,036). The piezoelectric materials used in such peristaltic pumps change shape in response to changes in applied voltage. As their shape changes, the changing shape acts to compress the fluid and provide a motive pumping force. The use of contacting seals in known piezoelectric peristaltic pumps, however, inherently limits them to operation at low differential pressure. The use of the piezoelectric material as the pump pressure boundary also limits known pumps to low internal pressure. Relative motion of the seal surfaces results in rapid wear and subsequent leakage. The dimensional tolerance required for proper operation also is beyond that of normal manufacturing methods. Finally, the full capability of the piezoelectric material is not utilized in such pumps since the relatively thick walls of the tube utilize only the piezoelectric effect in the direction of voltage application (the d₃₃ piezoelectric coefficient), while improved performance could be realized by also utilizing the piezoelectric effect perpendicular to the applied voltage (the d₃₁ and d₃₂ piezoelectric coefficients).

[0007] It is also known to use electrorheological fluid to control the pressure difference between the two ends of a hydraulic cylinder and thereby to restrict piston motion. The application of voltage across small spaces containing the ERF causes induced dipoles to form in the ERF, which aligns the particles and forms chains, resulting in changes in viscosity in the fluid, which can be used advantageously in the system design. Such known devices are inherently passive in that they can oppose external forces to reduce piston movement but do not generate internal forces that can cause output piston motion against the direction of external forces.

[0008] It is, therefore, one objective of the present invention to provide a peristaltic pump that is lightweight, compact, and highly scalable.

[0009] It is another objective of the present invention to provide a peristaltic pump that is completely reversible, operating equally well in either direction and having the ability to act as a valve when not pumping.

[0010] It is another objective of the present invention to provide a peristaltic pump that can produce the high differential pressure required in a hydraulic system.

[0011] It is another objective of the present invention to provide a peristaltic pump that can operate at the high internal pressure required in a hydraulic system.

[0012] It is another objective of the present invention to provide an integrated hydraulic actuation system incorporating a peristaltic pump into a hydraulic cylinder.

[0013] It is still another objective of the present invention to provide a piezoelectric peristaltic pump for ERF that utilizes the same electrodes and applied voltages for both piezoelectric activation and the ERF activation.

[0014] It is another objective of the present invention to provide a peristaltic pump that pumps fluid from both the inside and outside of the piezoelectric tube, significantly increasing pump volumetric capacity and output pressure.

[0015] It is another objective of the present invention to utilize the combine piezoelectric effect in the direction of voltage application (the d₃₃ piezoelectric coefficient) and perpendicular to the applied voltage (the d₃₁ and d₃₂ piezoelectric coefficients).

[0016] It is another objective of the present invention to provide a peristaltic pump that has a simple and inexpensive power supply.

[0017] It is another objective of the present invention to provide a simple and inexpensive power supply for substantially equal capacitive loads that operate in a step manner between two voltage states.

SUMMARY OF THE INVENTION

[0018] In order to achieve the foregoing objectives, the peristaltic pump of the present invention provides hydraulic pressure using peristaltic action acting on an ERF. The pump may be integrated into a hydraulic cylinder and used to force ERF from one side of the piston to the other thereby creating an actuator system. The ERF forms a traveling seal due to the effect of the voltage that is applied to cause the peristaltic action, eliminating the need for the check valves and control valves that are usually associated with hydraulic actuation systems, and eliminating the need for a contact seal. It further pumps ERF with both the inside and outside of the piezoelectric tube, increasing pump capacity and balancing the effects of differential pressure to increase the available output pressure. The present invention also provides an improved power supply for use in such a pump and other applications that require switching of capacitive loads between two voltage states.

[0019] One embodiment of the peristaltic pump of the present invention consists of three coaxial cylindrical components; a high-modulus rod contained within a piezoelectric tube, which in turn is contained within a cylindrical pressure casing, which may the casing of a hydraulic cylinder. The casing is filled with ERF. The piezoelectric tube has a plurality of electrode bands on its outer surface and is coated on its interior with an electrically conductive material. The electrodes are voltage-activated to cause certain portions of the tube to expand and others to contract, resulting in peristaltic action. The applied voltage also causes the ERF to form a gel state both inside and outside of the piezoelectric tube. The ERF in the gel state seals the pump and allows the pumping action to occur without the use of check valves or control valves. As the voltage is stepped along the piezoelectric tube the ERF is advantageously pumped from both the inside and outside of the tube, increasing the pump's capacity and balancing the differential pressure across the tube, allowing greater output pressure.

[0020] A second embodiment of the present invention uses an identical arrangement to the first embodiment, except that a second set of electrode bands is added to the interior of the casing, and a third set of electrode bands is added to the outside of the high-modulus rod. These additional electrode bands are the same width as, and in alignment with, the electrode bands on the piezoelectric tube. The electrodes on the piezoelectric tube are voltage-activated to cause certain portions of the tube to expand and others to contract resulting in peristaltic action. Voltage is also applied to the corresponding electrodes on the casing and on the high-modulus rod at the same magnitude and in step with the piezoelectric tube voltage but with the opposite polarity. This causes the ERF to be in a gel state only in the selected pump volume serving as a seal and is in the liquid state in the remaining pump volume. The seal “travels” as voltage is stepped along the tube.

[0021] The improved power supply of the present invention provides the stepped voltage to the electrode bands by taking advantage of the fact that each of the electrodes on the piezoelectric tube forms a capacitor with the piezoelectric material serving as the dielectric and the conductive layer on the tube interior as the other plate. The power supply switches the polarity of the electrodes in a stepped fashion by transferring the associated charge through an inductor and drawing lost energy from a voltage source.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The operative features of the present invention are explained in more detail with reference to the following drawings, in which reference numerals refer to like elements, and in which:

[0023]FIG. 1 is a cut away side view of the first embodiment of the peristaltic pump of the present invention;

[0024]FIG. 2 is a perspective view of the piezoelectric tube of the first embodiment of the peristaltic pump of the present invention;

[0025]FIG. 3 is a perspective view of the spacer of the peristaltic pump of the present invention;

[0026] FIGS. 4-11 are cut away side views of the first embodiment of the peristaltic pump of the present invention, showing the peristaltic pumping action;

[0027]FIG. 12 is a partially cut away side view of a hydraulic system incorporating the peristaltic pump of the present invention;

[0028]FIG. 13 is a cut away perspective view of the casing of the second embodiment of the peristaltic pump of the present invention;

[0029]FIG. 14 is a perspective view of the high modulus rod of the second embodiment of the peristaltic pump of the present invention;

[0030]FIGS. 15a and 15 b are schematic views of generalized capacitors used in explaining the operation of the power supply of the present invention;

[0031]FIGS. 16a-16 c are schematic views of circuits used in the power supply of the present invention;

[0032]FIG. 17 is a graph of the output of the voltage and current of the circuits of FIG. 16;

[0033]FIG. 18 is a schematic view of a circuit used in the power supply of the present invention,

[0034]FIG. 19 is a graph of the output of the voltage and current of the circuit of FIG. 19; and

[0035]FIG. 20 is a circuit diagram of the power supply of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0036] Turning first to FIGS. 1 and 2, the first embodiment of the peristaltic pump 10 of the present invention can be seen. Pump 10 comprises outer pressure casing 12 with ports 15 and 16, for the introduction and exit of electrorheological fluid (ERF) in communication with the rest of a hydraulic system. The pump of the present invention preferably is incorporated within a hydraulic system, as is described in more detail below, but may be used in any suitable fashion to which its characteristics are suited. Casing 12 encloses cylindrical piezoelectric tube 20, which is coaxial with the casing. Piezoelectric tube 20 comprises a suitable piezoelectric material, such as that discussed below. A plurality of electrode bands 22, which preferably are made of copper or another suitable conductor, encircle tube 20. Any suitable number may be used, eight are shown in this embodiment. They are applied to the tube by any suitable known technique, such as electroplating. Rod 18 is contained within, and coaxial with, tube 20, to create inner gap 23. Outer gap 21 is defined by the casing and the tube. The rod 18 comprises a high modulus and conducting material such as steel or aluminum. As can be seen, the casing, rod and tube are coaxial. A spacer 35 (see FIG. 3) supports the piezoelectric tube 20 and the rod 18 in coaxial alignment to maintain the inner gap 21 and outer gap 23. As can be seen in FIG. 3, spacer 35 has radial passages 36 for flow of the pumped ERF from the inlet port 15 or 16 though the inner gap 21 and outer gap 23 to the opposite outlet port. The spacer is preferable made from polytetrafluoroethylene (PTFE, marketed as TEFLON®, a registered trademark of E.I. du Pont de Nemours and Company), although other chemically compatible insulating materials can be used. As can be seen in FIG. 2, inner surface 23 of tube 20 is coated with an electrically conductive material, preferably of the same material as the outer electrodes 22. The casing is filled with a suitable ERF, such as that discussed below. Power supply 8 (shown schematically) connects to the pump via means 9, providing power to cause the peristaltic action and to activate the ERF, as is described in more detail below.

[0037] Dimensions and materials can be selected for compatibility with the target application. In one example, the tube was 5.0 cm (2.0 inches) long, with an outer diameter of 4.0 cm (1.6 inches), and a wall thickness of 0.25 cm (0.1 inches). In this example the tube material was MSI piezoelectric material PZT-5H, an isotropic ceramic prior to poling. Poling is accomplished by heating the ceramic to its Curie temperature and applying a DC field to the crystal to align the previously randomly oriented dipoles parallel to the field. Upon poling, the ceramic becomes an isotropic and exhibits directionally dependent piezoelectric and mechanical properties. A preferred ERF is Bridgestone's fluid ERF HP-2. This material has minimal settling with easy redispersion.

[0038] In operation, the first embodiment of the present invention works as follows, as can be seen by viewing FIGS. 4-11 in sequence, which show ERF being pumped from port 16 to port 15. Pumping in the opposite direction is done by reversing the sequence. The piezoelectric tube displacements shown in FIGS. 4-11 were calculated using a fully-coupled finite element analysis. The resulting displacements are shown with a scale factor of 100 to allow visualization of the displacements that are actually too small for the unaided eye to see. In these figures spacer 35 is not shown.

[0039] In FIG. 4, a positive voltage is applied to half of the tube outer electrodes via power supply 8 (not shown in all views) and connecting means 9, the preferred embodiment of which is discussed in more detail below, and a negative voltage is applied to the other half of the outer electrodes. The coated inner surface of the tube is not connected to the power supply and therefore is electrically floating. This positive/negative voltage differential is applied in a moving and repeatedly on-going fashion along the length of the tube, to create the peristaltic action of the present invention. This applied voltage may be generated and applied in any suitable fashion, for example, by the power supply disclosed in more detail below

[0040] As can be seen in FIG. 4, the portion of piezoelectric tube 20 that has the positive voltage applied (A) increases in thickness due to the d₃₃ effect but also contracts in diameter and shortens due to the d₃₁ and d₃₂ effects. The opposite effect can be seen taking place on the other half of the tube, where the negative voltage is applied (B), with the tube expanding and lengthening in that area. Due to the balance between the applied positive and negative voltages applied to the outer electrodes of the tube, the voltage on the inner electrode remains at zero. The magnitude of the tube displacement depends upon the ratio of the inner to outer tube diameters, with the displacement increasing as the ratio approaches one (i.e. a thin-walled tube). In general, a thin-walled tube has a greater capacity for fluid movement than a thick-walled tube but at a lower maximum differential pressure due to its increased compliance. One with ordinary skill in piezoelectric design is able to perform optimization of tube parameters for a particular application. For the above example tube, with an outer diameter of 4.0 cm (1.6 inches) and a wall thickness of 0.25 cm (0.1 inches), at a discharge pressure of 1.8 MPa (265 psi), the calculated pump displacement was 30 μl (0.002 cu-in) per cycle, with an applied voltage of plus and minus 1000 Volts (0.4 MV/m or 10 V/mil).

[0041] In addition to the stepping positive and negative voltage applied to the piezoelectric tube electrodes, a voltage of zero is applied to the tube casing 20 and a constant positive voltage is applied to the high modulus rod 18, preferably from the same power supply. Therefore the voltage applied to the tube electrodes, in addition to causing the peristaltic action as it is stepped down the tube, is felt across the fluid in the inner and outer gaps 21 and 23 between the tube and the rod and between the pressure casing and the tube, and causes the ERF to be in a continuous gel state in the inner and outer gaps 21 and 23. The activated gel is, in effect, “self-sealing,” having entered the pump in a liquid state, but becoming a semi-solid gel as it is pumped and subject to the applied voltage. The maximum differential pressure that can be developed by the ERF by is given by 2 τl/g where τ is the activated yield stress and l/g is the ratio of gap length to width. In the above example, with a piezoelectric tube length of 5 cm (2.0 inches) and a gap of 0.2 mm, the maximum differential pressure is 2.1 MPa (300 psi), when τ is equal to 4.2 kPa as it is at 800 Volts for the chosen ERF. The present invention uses the gel state as a seal to pump from the inside and the outside of tube 20, maximizing the system's pumping capacity, and eliminating the need for contact between the tube and the rod for sealing.

[0042] Turning next to FIG. 5, as can be seen, the applied voltage has advanced or stepped one step right to left, one step being in this case one outer electrode. The portion of tube that is contracted and shortened (A) has moved right to left by the width of one electrode, and a new contracted, shortened portion (A) has formed at the right with the application of negative voltage to the right outer electrode. The semi-solid ERF is pushed to the left due to the peristaltic action of tube 20, both outside the tube (21), and within the tube (23), with the ERF entering the pump through port 16 and exiting at port 15. As can be seen, the present invention advantageously pumps fluid from the interior and exterior of the tube, increasing the capacity of the pump. This arrangement also prevents the piezoelectric tube from forming any portion of the system pressure barrier and makes the pumping action independent of the hydraulic system pressure. Any internal pressure may be used as long as it is within the pressure containment capability of casing 20. This arrangement furthermore increases the differential pressure that may be achieved from pump inlet to outlet. The partial balance of differential pressure on the inside and outside of the piezoelectric tube means that available tube displacement capability is not used to overcome tube compliance, as is the case with one-sided operation

[0043] FIGS. 4-11 show a complete cycle of pump operation, which is repeated in a continuous fashion utilizing the same principles to create a continuous supply of a pressurized fluid at port 15, for example, to actuate a control surface. The action taking place in each figure is to be understood to be acting along the same principles as previously explained, and the series of figures exhibits the voltage stepping along the length of the tube. For example, in FIG. 6, the voltage has advanced one step further to the left. The peristaltic action combined with semi-solid ERF causes the ERF to be forced right to left, both within and without tube 20. It should be understood that peristaltic pumping action may be reversed at any time and the ERF forced in the opposite direction simply by reversing the direction of the voltage stepping. It should be further understood that the voltage stepping may be stopped at any time and the pump used as a valve by maintaining constant voltage on the outer electrodes. The ERF will under this condition remain in the gel state and provide resistance to flow through the pump that varies with the magnitude of the applied voltage. It further should be understood that the flow rate developed by the piezoelectric peristaltic pump is determined by the frequency of cycling though the illustrated voltage steps. The maximum operating frequency will depend upon the exact design used. For the above example piezoelectric tube, the maximum frequency is expected to be in excess of 3.3 kHz. This frequency will provide a volumetric flow rate of 100 cc/sec (6.1 cu-in/sec) at the calculated pump displacement of 30 μl (0.002 cu-in) per cycle. Lower frequencies may be used to obtain lower flow rates as desired.

[0044] Other patterns of electrode activation are possible in addition to those shown in FIGS. 4 to 11. For example, with a sufficient number of outer electrodes, two or more sealed cavities could be formed and moved by electrode voltage stepping to provide the fluid pumping. The only restriction is that positive and negative voltage be applied to an equal number of outer electrodes to maintain the advantage of requiring no electrode connection to the inner electroded surface. Still more patterns of electrode activation are available by providing and electrical connection to the inner electroded surface and maintaining this voltage at zero.

[0045]FIG. 12 is a cut away side view of an integrated hydraulic actuation system 50 incorporating a peristaltic pump of the present invention into a hydraulic cylinder. The hydraulic cylinder is of a conventional design except that it has no inlet or outlet ports. Casing 12 is filled with ERF 38, with seals 40 preventing leakage around actuation rod 45, which may be of any length. The high modulus rod 18 and insulating supporting plates 35 of pump 11 are attached to actuation rod 45 and move with it, forming a piston assembly. No piston seals are required as gap 21 is used in the pumping operation. Operation of the integrated hydraulic actuation system is identical to that described for the stand-alone piezoelectric pump above. Applied stepping voltages cause the tube 20 to pump fluid on both the inside (23) and outside (21) from one end of the tube to the other. The resulting volumetric changes force the piston assembly to move and thereby move the actuation rod 45. In the above example, at a volumetric flow rate of 100 cc/sec (6.1 cu-in/sec) and discharge pressure of 1.8 MPa (265 psi), the integrated hydraulic actuation system would provide an output force of 2300 N (520 lbf) at a rod speed of 8.0 cm/sec (3.1 in/sec).

[0046] It should be understood that the reversibility of the peristaltic pumping action results in the integrated hydraulic actuation system 50 being reversible as well. It should be further understood that the voltage stepping may be stopped at any time and the actuation rod 45 locked in position by maintaining constant voltage on the outer electrodes. The resistance of rod 45 to motion will under this condition vary with the magnitude of the applied voltage. Although incorporating a peristaltic pump into a hydraulic cylinder to create an integrated hydraulic actuation system obtains significant advantages, it should be understood that the to present invention be used as the external supply source for one or more conventional hydraulic cylinders.

[0047] A second embodiment of the present invention uses an identical arrangement to the first embodiment, except that a second set of electrode bands 45 is added to the interior of the casing 20, as is shown in FIG. 13, and a third set of electrode bands 46 is added to the outside of the high-modulus rod 18, as shown in FIG. 14. These additional electrode bands are the same width as, and in alignment with, the electrode bands on the piezoelectric tube. The electrodes on the piezoelectric tube are voltage-activated to cause certain portions of the tube to expand and others to contract resulting in peristaltic action as in the first embodiment. However, in the second embodiment, voltage is also applied to the corresponding electrodes on the casing and on the high-modulus rod, at the same magnitude, and in step with, the piezoelectric tube voltage, but with the opposite polarity. In this embodiment, the ERF is in the gel state only in a selected pump volume serving as a seal and is in the liquid state in the remaining pump volume. This seal “travels” along the length of the casing as voltage is stepped along the tube, and as the portion of the ERF that is in the gel state changes.

[0048] Although any suitable power supply may be used with the present invention, an improved power supply specifically for use with the present invention has been developed. To generate the stepping applied voltage required, the present invention provides a simple and inexpensive power supply that switches charge between the electrodes. It transfers charge to switch capacitive components between voltage states in an efficient manner. The electrical source required for the present invention is a stepping between two voltages without fine control, which is not necessary to operate the present invention, where the polarity is the electrodes is switched between positive and negative in an ongoing fashion.

[0049] By way of explanation, turning to FIGS. 15a and 15 b, a single capacitor 200 can be seen. At time t_(s) (FIG. 15a) the capacitor has a positive voltage on terminal A and a negative voltage on terminal B. At time t_(e) (FIG. 15b), the capacitor polarity has been reversed. Known switching technology can accomplish this result, but with significant energy loss, such as by use of a conventional switching amplifier or a switched capacitive amplifier. These devices also require large internal energy storage to hold capacitive charge during the polarity switch.

[0050]FIGS. 16a-16 c illustrate the approach of the power supply of the present invention to reverse polarity. At time t_(s) (FIG. 16a), capacitor 200 has a positive voltage on terminal A and a negative voltage on terminal B. Two switches (202 and 204) are closed (FIG. 16b) to connect inductor 206 across the capacitor terminals. Current starts to flow and reaches a maximum at time t_(m) (see FIG. 17), when the voltage at both terminals A and B is zero. At this point all of the circuit energy is stored in the inductor. The stored energy returns to the capacitor as the current drops. When the current reaches zero at time t_(e) the voltages are at their maximum, with the capacitor polarity reversed. The switches are then opened and the capacitor polarity remains as desired with a positive voltage at terminal B and a negative voltage at terminal A. The voltage and current relationship can be seen in FIG. 17.

[0051] This explanation applies only to components with zero losses—ideal components. In such components the process of exchanging the charge internally with the system without an outside power supply could go on indefinitely. In the pump of the present invention, the piezoelectric material, which has a high dielectric constant, forms a capacitive component when placed between the circular electrode and the inner coating. This “capacitive” component, however, is far from ideal and has electrical losses due to electrical energy conversion to work output and to heat. Therefore, a means for supplying energy must be provided in the power supply of the present invention.

[0052]FIG. 18 illustrates that in the present invention, a voltage source 208 with outputs V_(s) and V_(s) is added into the circuit to provide this energy. As seen in FIG. 19, voltage B starts the switch cycle with a value of −V_(s) and must equal V_(s) at the end. Voltage A is just the opposite. The reversal begins at time t_(s) and proceeds as before. However, due to losses, voltage B will only reach a lower value V₁ at time t₁. To compensate, the voltage source is switched into the circuit via switches 203 and 205 at time t_(p) and increases the voltage to V_(s). This action drops the current more rapidly and it reaches zero at time t_(e) to end the reversal. After the reversal there is no energy stored in the inductor and the same energy is stored in the capacitor as at the cycle start. Therefore, the voltage source must have provided exactly the energy needed to make up for losses.

[0053]FIG. 20 shows the power supply of the present invention, which provides stepping voltage to the electrode bands. Each of the electrode bands is represented as a capacitor 200 with the common inner surface forming the second plate of the capacitor. In this example, electrodes 1 through 4 have positive voltage and electrodes 5 through 8 are negative. The next voltage step requires electrodes 4 and 8 to switch polarity, as the voltage is stepped right to left. Closing the switches 201 for electrodes 4 and 8 as described in FIG. 17 above accomplishes this reversal, with the voltage source providing only the energy needed to make up for losses by the operation of switches 205 and 203. Note that only the switches 201 for electrodes 4 and 8 are involved in the step with all other switches 201 remaining open. The following step will involve switches 201 for electrodes 3 and 7 only and the step after that will involve switches 201 for electrodes 2 and 6 only. Note that a single inductor 206 and voltage source 208 provides stepping for all electrode bands.

[0054] Implementing the power supply of the present invention requires very few components. All switch components are preferably identical triacs (a triac is a thyristor that conducts in either direction when triggered and has symmetrical bidirectional blocking capability otherwise) since they possess exactly the characteristics needed. A triac conducts when triggered and blocks when current reaches zero. Therefore, all the switches automatically open (triacs blocking) when required without any control signal. Closing the switches (triggering the triacs) requires control circuitry (not shown, and any switch circuitry can be used). The individual electrode triacs will be triggered by pulses at the stepping frequency. The command stepping frequency will be an input to the ICE power supply, since it determines the actuator velocity for a given condition. Electrical components other than triacs may be used for the switches with more complicated stepping circuits required for triggering.

[0055] The present invention has been described in an illustrative manner. It should be evident that modifications may be made to the specific embodiments shown in the description without departing from the spirit and s cope of the present invention. Such modifications are considered to be within the scope of the present invention, which is limited solely by the scope and spirit of the appended claims. 

I claim:
 1. A peristaltic pump comprising: a pressure casing having first and second ends; a piezoelectric tube having first and second ends; said tube disposed within said casing; a high modulus rod have first and second ends; said rod disposed within said tube; spacers at said first and second ends of said tube and rod; said spacers maintaining said tube and rod in coaxial alignment; said rod and said tube defining a first annular gap therebetween; said casing and said tube defining a second annular gap therebetween; said casing filled with an electrorheological fluid.
 2. The pump of claim 1 further comprising a first plurality of electrode bands, said bands on the exterior of said tube.
 3. The pump of claim 1 further comprising a power supply, said power supply electrically connected to said pump.
 4. The pump of claim 1 wherein said spacers comprise fluid passages.
 5. The pump of claim 1 wherein said tube comprises an inner surface, said inner surface coated with an electrically conductive material.
 6. The pump of claim 1 wherein said casing comprises inlet and exit ports.
 7. The pump of claim 1 further comprising a second plurality of electrode bands, said bands on the interior surface of said casing.
 8. The pump of claim 1 further comprising a third plurality of electrode bands, said bands on the outer surface of said rod.
 9. A peristaltic pump comprising: a pressure casing having first and second ends; a piezoelectric tube having first and second ends; said tube disposed within said casing; a high modulus rod having first and second ends; said rod disposed within said tube; spacers at said first and second ends of said tube and rod; said spacer and maintaining said tube and rod in coaxial alignment; said rod and said tube defining a first annular gap therebetween; said casing and said tube defining a second annular gap therebetween; said casing filled with an electrorheological fluid; a first plurality of electrodes bands, said bands on the exterior of said tube; a second plurality of electrode bands; said bands on the internal surface of said casing; and a third plurality of electrode bands; said bands on the outer surface of said rod; and a power supply, said power supply electrically connected to said pump.
 10. The pump of claim 9 further comprising a power supply, said power supply electrically connected to said pump.
 11. The pump of claim 9 wherein said spacers comprises fluid travel passages.
 12. The pump of claim 9 wherein said tube comprises an inner surface; said inner surface coated with an electrically conductive material.
 13. The pump of claim 9 wherein said casing comprises inlet and exit ports.
 14. A hydraulic system comprising: a peristaltic pump; a pressure casing having first and second ends; said pump disposed within said casing; said casing filled with an electrorheological fluid; an actuator rod; said rod disposed within and passing through, the ends of said casing; said pump connected to said rod; said pump operable to actuate said rod.
 15. The system of claim 14, further comprising a plurality of support plates, said pump connected to said rod by said support plates.
 16. The system of claim 14 further comprising a power supply, said power supply electrically connected to said system.
 17. A power supply for use with an electrical system comprising: a plurality of capacitors; said capacitors electrically connected in parallel; a plurality of capacitor switches; an inductor; said plurality of capacitors connected in series with said inductor via said capacitor switches; and a voltage source; said voltage source connected across said inductor via first and second voltage switches.
 18. The power supply of claim 17 whereby said capacitors comprise an electrode band and a portion of a piezoelectric tube.
 19. The power supply of claim 17 wherein said capacitor switches are triacs.
 20. The power supply of claim 17 wherein said voltage switches are triacs. 